ALMA Reveals Teenage Years of New Worlds

New astronomical survey captures previously unknown growing pains in the lives of planets.

To the point

• New Discoveries: Astronomers have captured detailed images of young planetary systems, revealing their growth stages and complexities.
• Significant Findings: The ALMA survey provides insights into debris discs, which represent the formative phase of planet formation, akin to the teenage years of planetary systems.
• Historical Insights: The results highlight chaotic periods in planetary development, helping to understand the evolution of our Solar System.

Astronomers have captured the most detailed snapshot of planetary systems in an era long shrouded in mystery yet. The ALMA survey to Resolve exoKuiper belt Substructures (ARKS), using the Atacama Large Millimeter/submillimeter Array (ALMA), has produced the sharpest images ever of 24 debris discs, the dusty belts left after planets finish forming. These discs are the cosmic equivalent of the teenage years for planetary systems – somewhat more mature than newborn, planet-forming discs, but not yet settled into adulthood.

A missing link in planetary family albums

“We’ve often seen the ‘baby pictures’ of planets forming, but until now, the ‘teenage years’ have been a missing link," says Meredith Hughes, an Associate Professor of Astronomy at Wesleyan University, Middletown, Connecticut, USA and co-PI of this study.

“Debris discs are representing the collision-dominated phase of the planet formation process,” explains Thomas Henning, MPIA (Max Planck Institute for Astronomy) scientist and ARKS co-I. “With ALMA, we are able to characterise the disc structures pointing to the presence of planets. In parallel, with direct imaging and radial velocity studies, we are searching for young planets in these systems.”

Our own Solar System’s counterpart to this phase is the Kuiper Belt, a ring of icy debris beyond Neptune that preserves a record of massive collisions and planetary migrations from billions of years ago. By studying 24 exoplanetary debris belts, the ARKS team has opened a window into what our Solar System went through as the Moon was forming and as planets jostled for their final places, and sometimes trading orbits!

Teenage discs: hard to “photograph,” impossible to ignore

Debris discs are faint, hundreds or even thousands of times dimmer than the bright, gas-rich discs where planets are born. The ARKS team overcame these challenges and produced images of these discs in unprecedented detail. Like teenagers dodging the camera, these faint discs have managed to hide from astronomers for years. But thanks to ALMA, astronomers can now see their complex structures: belts with multiple rings, wide smooth halos, sharp edges, and even unexpected arcs and clumps.

However, ALMA, with its dozens of individual radio telescopes, does not take pictures in the classical sense. Instead, it collects radio signals emitted by dust particles and molecules, which have to be processed and correlated afterwards. Each telescope contributes to the final image, synthesised from the stream of radio waves.

"We’re seeing real diversity – not just simple rings, but multi-ringed belts, halos, and strong asymmetries, revealing a dynamic and violent chapter in planetary histories,” adds Sebastián Marino, program lead for ARKS, and an Associate Professor at the University of Exeter, UK.

Highlights and firsts from ARKS

• A New Benchmark: ARKS is the largest, highest-resolution survey of debris discs, akin to a ‘DSHARP-for-debris-discs’, setting a new gold standard.
• A Dynamic, Violent Youth: About one-third of observed discs show clear substructures (multiple rings or distinct gaps), suggesting legacy features left from earlier, planet-building stages or sculpted by planets over much longer timescales.
• Unexpected Diversity: While some discs inherit intricate structures from their earlier years, others mellow out and spread into broad belts, similar to how we expect the Solar System to have developed.
• Clues to Planetary ‘Stirring’: Many discs show evidence for zones of calm and chaos, with vertically “puffed-up” regions, akin to our Solar System’s own mix of serene classical Kuiper Belt objects and those scattered by Neptune’s long-ago migration.
• Surprising Gas Survivors: Several discs retain gas much longer than expected. In some systems, lingering gas may shape the chemistry of growing planets, or even push dust into wide halos.
• Asymmetries and Arcs: Many discs are lopsided, with bright arcs or eccentric shapes, hinting at gravitational shoves from unseen planets, leftover birth scars from planetary migration, or interactions between the gas and dust.
• Public Data Release: All ARKS observations and processed data are being made freely available to astronomers worldwide, enabling further discoveries.

Implications: your Solar System was once a wild ride

The ARKS results show this teenage phase is a time of transition and turmoil. “These discs record a period when planetary orbits were being scrambled and huge impacts, like the one that forged Earth’s Moon, were shaping young solar systems," says Luca Matrà, a co-PI on the survey, and Associate Professor at Trinity College Dublin, Ireland.

By looking at dozens of discs around stars of different ages and types, ARKS helped decode whether chaotic features are inherited, sculpted by planets, or arise from other cosmic forces. Answering these questions could reveal whether our Solar System’s history was unique, or the norm.

Looking ahead: hunting for planetary architects

The ARKS survey’s findings are a treasure trove for astronomers hunting for young planets and seeking to understand how planet families, like our own, are built and rearranged.

“This project gives us a new lens for interpreting the craters on the Moon, the dynamics of the Kuiper Belt, and the growth of planets big and small. It’s like adding the missing pages to the Solar System’s family album,” adds Hughes.

Background information

The ARKS survey is the work of an international team of approximately 60 scientists, led by the University of Exeter, UK; Trinity College Dublin, Ireland; and Wesleyan University, Middletown, Connecticut, USA. For more information, visit https://arkslp.org/.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

This press release was largely adapted from the original article published by NRAO.

MN